A wireless communication system typically includes a number of base stations that are configured to provide wireless coverage areas in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices (whether or not user operated), can operate. In turn, each base station could be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the system could engage in air interface communication with a base station and could thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Each coverage area in such a system could operate in accordance with a particular radio access technology, with air-interface communications from the base stations to UEs defining a downlink or forward link and air-interface communications from the UEs to the base stations defining an uplink or reverse link.
Over the years, the industry has embraced various “generations” of radio access technologies, in a continuous effort to increase available data rate and quality of service for end users. These generations have ranged from “1G,” which used simple analog frequency modulation to facilitate basic voice-call service, to “4G”—such as Long Term Evolution (LTE), which facilitates mobile broadband service using technologies such as orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO). And most recently, the industry is now exploring developments in “5G” and particularly “5G NR” (5G New Radio), which may use a scalable OFDM air interface, advanced channel coding, massive-MIMO, beamforming, and/or other features, to support higher data rates and countless applications, such as mission-critical services, enhanced mobile broadband, and massive Internet of Things (IoT).
In accordance with the radio access technology, each coverage area could operate on one or more carriers each defining one or more ranges of frequency spectrum and having a respective downlink channel for carrying communications from the base station to UEs and a respective uplink channel for carrying communications from the UEs to the base station. Such carriers could be frequency division duplex (FDD), in which the downlink and uplink channels are defined as separate respective ranges of frequency (each having a respective frequency bandwidth and center frequency), or time division duplex (TDD), in which the downlink and uplink channels are defined on a common range of frequency (having a particular bandwidth and center frequency) but are distinguished from each other through time division multiplexing, with certain time intervals being used for downlink communication and other time intervals being used for uplink communication. Further, the downlink channel and uplink channel of each carrier could also be divided into respective sub-channels for carrying particular communications, such as one or more control channels for carrying control signaling and one or more traffic channels for carrying application-layer data and other traffic.
In an example system, for instance, the air interface could be divided over time into frames and subframes each defining a number of slots, and the uplink and downlink channels could each be divided over their frequency bandwidth into subcarriers that are grouped within each slot into physical resource blocks (PRBs) for carrying bearer traffic, and with portions of each subframe further defining various control channels for signaling communication between the base station and UEs.